DE69329811T2 - Capsule toner for heat and pressure fixation and process for its production - Google Patents

Description

The present invention relates to a heat and pressure fixing capsule toner used for developing electrostatic latent images in electrophotography, electrostatic printing and electrostatic recording, and a process for producing such a capsule toner.

As described in US-A-2297691 and US-A-2357809 and other publications, conventional electrophotography comprises the steps of forming an electrostatic latent image by uniformly charging a photoconductive insulating layer and then exposing the layer to eliminate the charge at the exposed portion, and making the formed image visible by adhering a colored, charged fine powder known as a toner to the latent image (a developing process); transferring the resulting visible image to an image-receiving layer such as a transfer paper (a transfer process); and permanently fixing the transferred image by heating, applying pressure or other suitable means of fixing (a fixing process).

As stated above, a toner must meet the requirements not only in the development process, but also in the transfer process and the fixing process.

In general, a toner is subjected to mechanical frictional forces by the shearing force and impact force during mechanical operation in a developing device, and suffers deterioration after copying several thousand to several tens of thousands of sheets. Such deterioration of the toner can be avoided by using a tough resin having such a high molecular weight that it can withstand the above mechanical friction. However, this kind of resin generally has such a high softening point that the obtained toner cannot be sufficiently fixed by a non-contact method such as oven fixing or radiation fixing with infrared rays because of its poor thermal efficiency. Further, when the toner is fixed by a contact fixing method such as a heat and pressure fixing method using a heat roller, which has excellent thermal efficiency and is therefore widely used, it becomes necessary to increase the temperature of the heat roller in order to achieve sufficient fixation of the toner, which brings about disadvantages such as deterioration of the fixing device, curling of the paper and increase in energy consumption. In addition, the resin described above has poor grindability, which significantly reduces the production efficiency of the toner in the production of the toner. Accordingly, the binder resin having too much increased degree of polymerization and too high softening point cannot be used.

Meanwhile, according to the heat and pressure fixing method using a heat roller, the surface of a heat roller comes into contact with the surface of a visible image formed on an image receiving sheet under pressure so that the thermal efficiency is excellent, and therefore is widely used in various copiers from high-speed copiers to low-speed copiers. However, when the surface of a heat roller comes into contact with the surface of the visible image, the toner tends to cause a so-called "offset phenomenon" in which the toner adheres to the surface of the heat roller and is thus transferred to a subsequent transfer paper. In order to prevent the phenomenon, the surface of a heat roller is coated with a material excellent in release properties such as a fluororesin, and a release agent such as a silicone oil is additionally applied thereto. However, the process of applying a silicone oil requires a larger scale fixing device, which is not only expensive but also complicated, which in turn may undesirably be the cause of various problems.

Although methods for improving the offset phenomenon by unsymmetricalizing or crosslinking the resins have been disclosed in JP-B-493/1982, JP-A-44836/1975 and JP-A-37353/1982, the fixing temperature has not yet been improved by these methods.

Since the lowest fixing temperature of a toner is generally between the temperature of the low-temperature offset of the toner and the temperature of its high-temperature offset, the range of the use temperature of the toner is between the lowest fixing temperature and the temperature of the high-temperature offset. Accordingly, by lowering the lowest fixing temperature as much as possible and increasing the temperature causing high-temperature offset as much as possible, the usable fixing temperature can be lowered and the usable temperature range can be widened, enabling energy saving, high-speed fixing and prevention of paper curling.

For the above reasons, the development of a toner with excellent fixability and offset resistance has always been desired.

A method for achieving low-temperature fixation by using an encapsulated toner comprising a core material and a shell formed thereon so as to cover the surface of the core material has been proposed.

Among such toners, those having a core material made of a low-melting wax that is easily plastically deformed as described in US-A-3,269,626, JP-B-15876/1971, JP-B-9880/1969, JP-A-75032/1973 and JP-A-75033/1973 have poor fixing strength and therefore can only be used in limited areas, although they can be fixed using pressure alone.

Further, as for toners having a liquid core material, if the shell strength is low, the toners tend to break in the developing device and discolor the inside thereof, even though they can be fixed only by pressure. On the other hand, if the shell strength is high, a higher pressure is required to break the capsule, resulting in too glossy images. Thus, it has been difficult to adjust the shell strength.

Further, as a toner for heat and pressure fixation, a capsule toner for heat roller fixation has been proposed which comprises a core material made of a resin having a low glass transition temperature, which serves to increase the fixing strength although blocking may occur at a high temperature when used alone, and a shell made of a resin wall having a high melting point, which is formed by interfacial polymerization, to impart blocking resistance to the toner. However, in JP-A-56352/1986, this toner cannot fully exhibit the property of the core material because the melting point of the shell material is too high, and also the shell is too tough and not easily broken. With the same reasoning as described above, capsule toners for heat roller fixing with improved fixing strength of the core material have been proposed (see JP-A-205162/1983, JP-A-205163/1983, JP-A-128357/1988, JP-A-128358/1988, JP-A-128359/1988, JP-A-128360/1988, JP-A-128361/1988 and JP-A-128362/1988). However, since these toners are produced by a spray drying process, more demanding is placed on the facilities for producing them. In addition, they cannot fully exhibit the properties of the core material because they do not provide a solution to the problems with the shell.

Further, in the capsule toner proposed in JP-A-281168/1988, the shell is made of a thermotropic liquid crystal polyester, and in the capsule toner proposed in JP-A-184358/1992, a crystalline polyester is used. Since each of the polyesters used in these references is not amorphous, the resin has a sharp melting point. However, the energy required for melting is high.

Furthermore, Tg of the core material is also high, which makes the fixability of the obtained toner poor.

Also, as methods for encapsulation proposed in JP-A-128357/1988, there are listed methods such as an immersion method using a solvent, a spray drying method and a fluidized bed method, all of which have problems in that they require complicated processes.

JP-A-162355/1990 discloses a capsule toner comprising a shell made of a polyester resin derived from a condensation reaction between biphenols and polyvalent carboxylic acids or suitable derivatives thereof. Further, attempts have been made to adjust the chargeability of the capsule toner in the presence of a charge control agent in the shell of the capsule toner or on the surface of the capsule toner. However, in the development process, the charge control agent is detached from toner by friction with carrier and adheres to the carrier, which reduces the triboelectric charge of the resulting toner, causing such problems as background contamination and scattering of the toner in the developing device. In addition, if no charge control agents are present on the surface of the toner, the charging speed may be low depending on the type of carrier, thereby causing background contamination or scattering of the toner in the case of high-speed printing.

An object of the present invention is to provide a capsule toner for heat and pressure fixation which has excellent offset resistance, is fixable even at low temperature and has excellent blocking resistance when the capsule toner is used for heat and pressure fixation using a heated roller.

Another object of the present invention is to provide a method for producing such a capsule toner.

Therefore, as a result of extensive studies with respect to solving the above-mentioned problems, the inventors have found that a capsule toner for heat and pressure fixing can form long-lasting clear visible images free from background contamination over a large number of copies when an amorphous polyester resin is used as the main component of the shell of the capsule toner, and thus have developed the present invention.

In particular, the present invention relates to a capsule toner for heat and pressure fixing according to claim 1 and a method for producing a capsule toner for heat and pressure fixing according to claim 10.

The capsule toner according to the invention is characterized in that the shell comprises an amorphous polyester as a main component. The main component mentioned here of the shell means that the amorphous polyester is an essential component in the material forming the shell, including the case where the material forming the shell consists exclusively of the amorphous polyester.

The amorphous polyester used in the present invention can be generally obtained by condensation polymerization between at least one alcohol monomer selected from divalent alcohol monomers and trivalent or higher polyvalent alcohol monomers and at least one carboxylic acid monomer selected from dicarboxylic acid monomers and tricarboxylic acid or higher polycarboxylic acid monomers. Among them, the amorphous polyesters obtained by condensation polymerization of monomers containing a divalent alcohol monomer and a dicarboxylic acid monomer and further containing at least one trivalent or higher polyvalent alcohol monomer and/or a tricarboxylic acid or higher polycarboxylic acid monomer are suitably used:

Examples of the dihydric alcohol components include bisphenol A-alkylene oxide adducts such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxyethylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane; Ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethane oil, dipropylene glycol, polyethylene glycol, polypropylene glycol, hydrogenated bisphenol A and other dihydric alcohols.

Examples of the trihydric or higher polyhydric alcohol components include sorbitol, 1,2,3,6-hexanetrol, 1,4-sorbitan, pentaerythritol, 1,2,4-butanetriol, glycerin, 2-methylpropanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and other trihydric or higher polyhydric alcohols. Among these, the trihydric alcohols are preferably used.

In the present invention, these dihydric alcohol monomers and trihydric or higher polyhydric alcohol monomers may be used individually or in combination.

Regarding the acid components, examples of the dicarboxylic acid components include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n-dodecenylsuccinic acid, n-dodecylsuccinic acid, n-octylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid and acid anhydrides thereof, lower alkyl esters thereof and other dicarboxylic acids.

Examples of the tricarboxylic acid or higher polycarboxylic acid components include 1,2,4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid and pyromellitic acid and acid anhydrides thereof, lower alkyl esters thereof and other tricarboxylic acids or higher polycarboxylic acids.

In the present invention, among these carboxylic acid components, the tricarboxylic acids or derivatives thereof are preferred. These dicarboxylic acid monomers and tricarboxylic acid or higher polycarboxylic acid monomers may be used singly or in combination.

The method for producing an amorphous polyester is not particularly limited in the present invention, and the amorphous polyester can be produced by esterification or transesterification of the above monomers.

Here, "amorphous" refers to those polymers that do not have a specific melting point. When a crystalline polyester is used in the present invention, the energy required for melting is large, whereby the fixability of the toner becomes undesirably poor.

In the amorphous polyester thus obtained, the glass transition temperature is 50 to 80°C, preferably 55 to 70°C. If the glass transition temperature is less than 50°C, the storage stability of the toner becomes poor, and if it exceeds 80°C, the fixability of the obtained toner becomes undesirably poor. In the present invention, the "glass transition temperature" used herein refers to the temperature of an intersection of the extension of the base line of not more than the glass transition temperature and the tangent showing the maximum rise between the beginning of the peak and its top, determined using a differential scanning calorimeter ("DSC Model 200", manufactured by Seiko Instruments, Inc.) at a temperature raising rate of 10°C/min.

Also, the acid value of the above amorphous polyester is preferably 3 to 50 KOH mg/g, more preferably 10 to 30 KOH mg/g. If it is less than 3 KOH mg/g, the shell comprising the amorphous polyester is less likely to be formed on the core material during in-situ polymerization, whereby the storage stability of the toner becomes poor, and if it exceeds 50 KOH mg/g, the toner tends to transition to a water phase, whereby the production stability becomes poor. Here, the acid value was measured according to JIS K0070.

The capsule toner of the present invention contains the above amorphous polyester as a main component in the shell materials, and as other shell-forming materials, a copolymer having one or more acid anhydride groups, a polyamide, a polyesteramide, a polyurea and a polyurethane can be used.

Examples of the copolymers having one or more acid anhydride groups used in the present invention include a copolymer obtained by copolymerizing one α,β-ethylenically copolymerizable monomer (A) having an acid anhydride group and the other α,β-ethylenically copolymerizable monomer (B).

Here, examples of the α,β-ethylenically copolymerizable monomers (A) having an acid anhydride group include itaconic anhydride, crontonic anhydride and the compounds represented by the following formula:

in which Q₁ and Q₂ independently represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms or a halogen atom, which can be exemplified by maleic anhydride, citraconic anhydride, 2,3-dimethylmaleic anhydride, chloromaleic anhydride and bromomaleic anhydride, with maleic anhydride and citraconic anhydride being preferred.

Examples of the other α,β-ethylenically copolymerizable monomers (B) include styrene and styrene derivatives such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene and vinylnaphthalene; ethylenically unsaturated monoolefins such as ethylene, propylene and isobutylene; vinyl esters such as vinyl chloride and vinyl acetate; ethylenic monocarboxylic acids and esters thereof, such as acrylic acid, methyl acrylic ester, ethyl acrylic ester, n-propyl acrylic ester, isopropyl acrylic ester, n-butyl acrylic ester, isobutyl acrylic ester, n-octyl acrylic ester, isooctyl acrylic ester, decyl acrylic ester, lauryl acrylic ester, 2-ethylhexyl acrylic ester, stearyl acrylic ester, 2-hydroxyethyl acrylic ester, glycidyl acrylic ester, phenyl acrylic ester, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, decyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, Stearyl methacrylate, methacrylic acid-2-hydroxyethyl methacrylate, glycidyl methacrylate and phenyl methacrylate; substituted monomers with ethylenic monocarboxylic acids such as acrylonitrile, methacrylonitrile and acrylamide; ethylenic dicarboxylic acids and substituted monomers therewith such as dimethyl maleate. Among these monomers, styrene and (meth)acrylate are preferred from the viewpoint of high reactivity.

Preferred examples of such copolymers include a copolymer obtained by copolymerizing maleic anhydride and styrene, a copolymer obtained by copolymerizing maleic anhydride, styrene and (meth)acrylate, a copolymer obtained by copolymerizing citraconic anhydride and styrene, a copolymer obtained by copolymerizing citraconic anhydride, styrene and (meth)acrylate, a copolymer obtained by copolymerizing styrene and acrylonitrile, and a copolymer obtained by copolymerizing styrene, (meth)acrylate and acrylonitrile.

The copolymer used in the present invention can be obtained by a copolymerization reaction between 5 to 95 parts by weight of the above-described α,β-ethylenically copolymerizable monomer (A) having an acid anhydride group and 95 to 5 parts by weight of the other α,β-ethylenically copolymerizable monomer (B). The copolymerization reaction can be carried out by conventional addition polymerizations, but is not limited to these methods. Also, as for each of the above-described monomers (A) and (B), two or more kinds of them can be used to prepare a copolymer.

Also, the glass transition temperature of this copolymer is preferably not less than 60°C, more preferably not less than 80°C.

The above copolymer may be used alone or in a combination of two or more kinds.

In the present invention, the above-described copolymer having one or more acid anhydride groups is used together with the above-mentioned amorphous polyester. In this case, the content of the copolymer is preferably 2 to 10% by weight based on the amorphous polyester.

As described above, the use of the copolymer having one or more acid anhydride groups as a component of the shell in addition to the amorphous polyester brings advantages in that the triboelectric charge of the toner can be freely adjusted and that the distribution of the triboelectric charge is achieved.

In the present invention, the amorphous polyester described above can be used as the main component of the shell, the content of which is normally 50 to 100% by weight based on the total weight of the shell. Here, other components such as polyamides, polyesteramides, polyurethanes and polyureas can be contained in the shell in an amount of 0 to 50% by weight.

In producing the capsule toner of the present invention by the in-situ polymerization method, since each component used for shell materials, such as amorphous polyester, is to be dissolved in the monomers of the resin constituting the core material, solubility in the monomers is required.

As described above, by using the amorphous polyester as the main component of the shell and additionally using the copolymer having one or more acid anhydride groups, separation of the charge control agent from the toner by friction with the carrier does not tend to occur, thus enabling stably forming clear images free from background contamination over a large number of copies. Also, blocking resistance can be improved while maintaining good low-temperature fixability. The capsule toner of the present invention described above is normally a toner having a negative charge because the amorphous polyester used as the main component of the shell is normally negatively charged. However, in another embodiment of the present invention, it is also possible to provide a toner having a positive charge by using a certain amorphous polyester having a positive charge as the main component of the shell. In particular, as the amorphous polyesters having a positive charge, those having tertiary amine groups can be used. In this case, as other materials forming the shell, for example, the amorphous polyesters having no tertiary amine groups or the copolymers having one or more acid anhydride groups such as the styrene/maleic anhydride copolymer described above can be used to adjust the triboelectric charge. In addition, a small amount of polyamides, polyesteramides, polyurethanes or polyureas can also be used together therewith.

More specifically, in the present invention, two embodiments are provided with respect to the amorphous polyesters: one has no tertiary amine groups, as described in detail above, and the other has tertiary amine groups, as described in detail below.

In the present invention, the amorphous polyester having tertiary amine groups is obtained by condensation polymerization of a monomer mixture containing a divalent or higher polyvalent alcohol monomer having one or more tertiary amine groups and/or a dicarboxylic acid or higher polycarboxylic acid monomer having one or more tertiary amine groups as monomers having a tertiary amine group. In the present invention, the condensation polymerization is preferably carried out using a monomer having one or more tertiary amine groups in an amount of 1 to 30 mol% based on the total monomers and a divalent or higher polyvalent alcohol monomer having no tertiary amine groups and/or a dicarboxylic acid or higher polycarboxylic acid monomer having no tertiary amine groups in an amount of 99 to 70 mol% based on the total monomers. When the amount of the monomer having one or more tertiary amine groups used is less than 1 mol% based on the total monomers, sufficient effects of the positive charge of the polyester which is generally negatively charged cannot be obtained, and if it exceeds 30 mol%, the moisture resistance of the toner becomes poor.

Incidentally, although the component having a primary or secondary amine group has little effect on achieving a positive triboelectric charge, since an amide is more easily formed during the condensation polymerization reaction, a small amount of such a component may be contained in the monomer mixture.

In the present invention, the carboxylic acid monomers are generally monomers of carboxylic acids, anhydrides thereof and lower alkyl esters thereof. Here, the lower alkyl esters are those having an alkyl group having 1 to 4 carbon atoms.

Examples of the monomers having one or more tertiary amine groups which can be used in the present invention include one or more kinds selected from divalent or higher polyvalent alcohol monomers and dicarboxylic acid or higher polycarboxylic acid monomers having the chemical structures of the following general formulas (I), (IIA), (IIB) and (III) in the molecule and the divalent or higher polyvalent alcohol monomers of the general formula (IV).

Here, R₁, R₂, R�5, R�7, R�8, R�9, R₁₀, R₁₁₇, R₁₁₇, R₁₄, R₁₁₇, R₁₄, R₁₃, R₁₄ and R₁₆ independently represent a hydrocarbon group having 1 to 15 carbon atoms; R₃ and R₄ independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R₆ represents an alkyl group including a cycloalkyl group, or an alkylene group including a cycloalkylene group, wherein the cycloalkyl or cycloalkylene group preferably has 5 to 10 carbon atoms; R₁₅ represents an alkyl group having 1 to 3 carbon atoms or the following group;

R₁₇ and R₁₅ independently represent an alkyl radical having 1 to 4 carbon atoms, wherein

R₁₇ and R₁₈ may form a heterocyclic ring with the nitrogen atom; and X represents a hydrogen atom or a hydroxyl group.

In the general formulas (I), (IIA), (IIB), (III) and (IV), the hydrocarbon groups represented by R₁, R₂, R₅, R₇, R₆, R₈, R₃, R₄, R₁₀, R₁₆, R₁₄, R₁₃, R₁₄ and R₁₆ have 1 to 15 carbon atoms, which may be the same or different, include aliphatic groups such as alkylene groups having a linear or branched chain, an aromatic ring or a saturated alicyclic ring, the aromatic or alicyclic ring preferably having 5 to 10 carbon atoms. The hydrocarbon groups represented by R₃ and R₄ include alkylene groups having 1 to 15 carbon atoms, which may be the same or different. The alkyl groups having 1 to 10 carbon atoms represented by R₁, which may be the same or different, include those having a linear or branched chain. The alkyl group or alkylene group having 1 to 10 carbon atoms represented by R₁, includes those having a linear or branched chain. The alkyl groups having 1 to 3 carbon atoms represented by R₁₇, include those having a linear or branched chain. The alkyl groups having 1 to 4 carbon atoms represented by R₁₇ and R₁₈, which may be the same or different, include those having a linear or branched chain, wherein R₁₇ and R₁₈ may form a heterocyclic ring with the nitrogen atom, and the same applies when R₁₅ is represented by

is represented. X also represents a hydrogen atom or a hydroxyl group.

In particular, the compounds include those specified in the following points (1) - (7).

(1) Examples of the glycols having the chemical structure of the general formula (I) include N,N'-bis(hydroxymethyl)piperazine, N,N'-bis(2-hydroxyethyl)-2,5-dimethylpiperazine and N,N'-bis(2-hydroxy-2-methylpropyl)piperazine.

(2) Examples of the dicarboxylic acids or lower alkyl esters thereof having the chemical structure of the general formula (I) include N,N-bis(carboxymethyl)piperazine and N,N'-bis(carboxyethyl)piperazine and the lower alkyl esters thereof.

(3) Examples of the alcohols having the chemical structure of the general formulas (IIA) and (IIB) include N,N-bis(2-hydroxyethyl)methylamine, N,N-bis(2-hydroxyethyl)cyclohexylamine and triethanolamine.

(4) Examples of the carboxylic acids or the lower alkyl esters thereof having the chemical structure of the general formulas (IIA) and (IIB) include N,N-bis(carboxymethyl)methylamine, N,N-bis(2-carboxyethyl)methylamine and nitriletriacetic acid and the lower alkyl esters thereof.

(5) Examples of the glycols having the chemical structure of the general formula (III) include 2-methyl-2-N,N-dimethylaminomethyl-1,3-propanediol and 2-methyl-2-N,N- diethylaminomethyl-1,3-propanediol.

(6) Examples of the dicarboxylic acids or the lower alkyl esters thereof having the chemical structure of the general formula (III) include 4-methyl-4-N,N-dimethylaminomethylazelaic acid and 5-methyl-5-N,N-diethylaminoethylundecanedioic acid and the lower alkyl esters thereof.

(7) Examples of the alcohols represented by the general formula (IV) include N,N'-dimethyl- N,N'-bis(2-hydroxyethyl)ethylenediamine and N,N'-dibutyl-N,N'-bis(2-hydroxypropyl)pentamethylenediamine.

In the present invention, these divalent or higher polyvalent alcohol monomers having one or more tertiary amine groups or dicarboxylic acid or higher polycarboxylic acid monomers having one or more tertiary amine groups may be used singly or in a combination of two or more. Particularly preferred are N,N-bis(2-hydroxyethyl)methylamine, piperazine derivatives, triethanolamine and nitrile triacetic acid.

In this embodiment, the divalent or higher polyvalent alcohol monomers without tertiary amine groups and the dicarboxylic acid or higher polycarboxylic acid monomers without tertiary amine groups may be the same as those described above in the Production of the usual amorphous polyester without tertiary amine groups mentioned.

The method for producing an amorphous polyester having tertiary amine groups in the present invention is not particularly limited, and the amorphous polyester can be produced by esterification or transesterification using the monomer mixtures containing the above monomers having one or more tertiary amine groups. At this time, the polymerization reaction can be carried out by mixing all the monomer components simultaneously at the beginning. Alternatively, the polymerization reaction can be carried out by introducing those monomers having one or more tertiary amine groups into the reaction system during the progress of the polymerization reaction to adjust the content of the tertiary amine groups in the amorphous polyester.

In the thus obtained amorphous polyester of the second embodiment, the glass transition temperature is 50°C to 80°C, preferably 55°C to 70°C, as in the case of the first embodiment, i.e., the amorphous polyesters having no tertiary amine groups. Also, the acid value of the above amorphous polyester (the second embodiment) is preferably 1 to 50 KOH mg/g, more preferably 5 to 30 KOH mg/g. If it is less than 1 KOH mg/g, the shell comprising the amorphous polyester is less likely to form on the core material during in-situ polymerization, thus making the storage stability of the toner poor, and if it exceeds 50 KOH mg/g, the polyester is likely to transition to a water phase, which deteriorates the production stability.

Further, the amine value of the above amorphous polyester (the second embodiment) is 2 to 25 KOH mg/g. If the amine value is less than 2 KOH mg/g, sufficient effects of positively charging the polyester cannot be obtained, and if it exceeds 25 KOH mg/g, the moisture resistance of the toner becomes poor. The amine value is measured according to the method ASTM D-2073-66.

In the present invention, the above-described amorphous polyester having tertiary amine groups can be used as the main component of the shell, the content of which is normally 50 to 100% by weight based on the total weight of the shell as in the amorphous polyester in the first embodiment. Here, other components such as polyamides, polyesteramides, polyurethanes and polyureas can be contained in the shell in an amount of 0 to 50% by weight.

The amorphous polyester of the first embodiment can be used in combination with that of the second embodiment. Two cases can occur, namely that the toner is positively charged and that the toner is negatively charged.

In the case of the toner being positively charged, the amorphous polyester of the second embodiment is added in an amount of not less than 50% by weight of the total amount of the amorphous polyesters. In the case of the toner being negatively charged, the amorphous polyester of the second embodiment is added in an amount of less than 50% by weight so that the amount of electric charge can be adjusted.

The resins to be used as the main components of the heat-fusible core materials (thermoplastic core materials) for the capsule toner of the present invention include thermoplastic resins such as polyester-polyamide resins, polyamide resins and vinyl resins, with vinyl resins being preferred. The glass transition temperatures attributable to the thermoplastic resin used as the main component of the above-described heat-fusible core material are 10°C to 50°C, more preferably 20°C to 40°C. If the glass transition temperature is lower than 10°C, the storage stability of the capsule toner becomes poor, and if it exceeds 50°C, the fixing ability of the resulting capsule toner becomes undesirably poor.

Among the above-mentioned thermoplastic resins, examples of the monomers constituting the vinyl resins include styrene and its derivatives such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene and vinylnaphthalene; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; vinyl esters such as vinyl chloride and vinyl acetate; ethylenic monocarboxylic acids and esters thereof, such as acrylic acid, methyl acrylic ester, ethyl acrylic ester, n-propyl acrylic ester, isopropyl acrylic ester, n-butyl acrylic ester, isobutyl acrylic ester, n-octyl acrylic ester, isooctyl acrylic ester, decyl acrylic ester, lauryl acrylic ester, 2-ethylhexyl acrylic ester, stearyl acrylic ester, 2-hydroxyethyl acrylic ester, glycidyl acrylic ester, phenyl acrylic ester, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, isooctyl methacrylate, decyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate; substituted monomers with ethylenic monocarboxylic acids such as acrylonitrile, methacrylonitrile and acrylamide; ethylenic dicarboxylic acids and substituted monomers therewith such as dimethyl maleate; and N-vinyl compounds such as N-vinylpyrrole and N-vinylpyrrolidone.

Among the above components constituting the core material resin according to the present invention, it is preferable that styrene or its derivatives are used in an amount of 50 to 90% by weight to form the main chain of the resins, and that the ethylenic monocarboxylic acid or esters thereof are used in an amount of 10 to 50% by weight to adjust the thermal properties such as the softening point of the resin so that the glass transition temperature of the core material resin can be easily adjusted.

When a crosslinking agent is added to the monomer composition comprising the core material-forming resin according to the present invention, any known crosslinking agent can be suitably used. Examples thereof include divinylbenzene, divinylnaphthalene, polyethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, 1,6-hexylene glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate and diallyl phthalate, with divinylbenzene and polyethylene glycol dimethacrylate being preferred. These crosslinking agents may be used alone or in a combination of two or more, if necessary.

The amount of the crosslinking agents used is preferably 0.001 to 15% by weight, more preferably 0.1 to 10% by weight, based on the polymerizable monomers. If the amount of these crosslinking agents used is more than 15% by weight, the resulting toner tends not to melt under heat, resulting in poor heat fixability and poor heat and pressure fixability. In contrast, if the amount used is less than 0.001% by weight, in heat and pressure fixing, a part of the toner cannot be completely fixed on a paper but rather adheres to the surface of a roller, which in turn is transferred to a subsequent paper, i.e., an offset phenomenon occurs.

A grafted or crosslinked polymer prepared by polymerizing the above monomers in the presence of an unsaturated polyester can also be used as a resin for the core material.

Examples of the polymerization initiators to be used in the preparation of the thermoplastic resin for the core material include azo and diazo polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile) and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile; and peroxide polymerization initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, isopropyl peroxycarbonate, cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide and dicumyl peroxide.

For adjusting the molecular weight or molecular weight distribution of the polymer or for adjusting the reaction time, two or more polymerization initiators may be used in combination. The amount of the polymerization initiator used is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of the monomers to be polymerized.

In the present invention, the charge control agent may additionally be added to the core material. Negative charge control agents to be added are not particularly limited, and examples thereof include metal-containing azo dyes such as "Varifast Black 3804" (manufactured by Orient Chemical), "Bontron S-31" (manufactured by Orient Chemical), "Bontron S-32" (manufactured by Orient Chemical), "Bontron S-34" (manufactured by Orient Chemical) and "Aizenspilon Black TVH" (manufactured by Hodogaya Kagaku); copper phthalocyanine dye; metal complexes of alkyl derivatives of salicylic acid such as "Bontron E-81" (manufactured by Orient Chemical), "Bontron E-82" (manufactured by Orient Chemical) and "Bontron E-85" (manufactured by Orient Chemical); and quaternary ammonium salts such as "Copy Charge NX VP434" (manufactured by Hoechst); and nitroimidazole derivatives, with Bontron S-34 being preferred .

The positive charge control agents are not particularly limited, and examples thereof include nigrosine dyes such as "Nigrosine Base EX" (manufactured by Orient Chemical), "Oil Black BS" (manufactured by Orient Chemical), "Oil Black SO" (manufactured by Orient Chemical), "Bontron N-O1" (manufactured by Orient Chemical), "Bontron N-07" (manufactured by Orient Chemical) and "Bontron N-11" (manufactured by Orient Chemical); triphenylmethane dyes containing tertiary amines as side chains; quaternary ammonium salt compounds such as "Bontron P-51" (manufactured by Orient Chemical), cetyltrimethylammonium bromide and "Copy Charge PX VP435" (manufactured by Hoechst); polyamine resins such as "AFP-B" (manufactured by Orient Chemical); and imidazole derivatives, with Bontron N-07 being preferred.

The above charge control agents may be contained in the core material in an amount of 0.1 to 8.0 wt%, preferably 0.2 to 5.0 wt%.

If necessary, the core material may contain one or more suitable offset inhibitors for improving offset resistance in heat and pressure fixation, and examples of the offset inhibitors include polyolefins, metal salts of fatty acids, fatty acid esters, partially saponified fatty acid esters, higher fatty acids, higher alcohols, paraffin waxes, amide waxes, polyhydric alcohol esters, silicone varnish, aliphatic fluorocarbons and silicone oils.

Examples of the above polyolefins include resins such as polypropylene, polyethylene and polybutene, which have softening points of 80 to 160°C. Examples the above metal salts of fatty acids include metal salts of maleic acid with zinc, magnesium and calcium; metal salts of stearic acid with zinc, cadmium; barium, lead, iron, nickel, cobalt, copper, aluminum and magnesium; divalent lead stearate; metal salts of oleic acid with zinc, magnesium, iron, cobalt, copper, lead and calcium; and mixtures thereof. Examples of the above fatty acid esters include ethyl maleate, butyl maleate, methyl stearate and ethylene glycol montanate. Examples of the above partially saponified fatty acid esters include montanate esters partially saponified with calcium. Examples of the above higher fatty acids include dotlecanic acid, lauric acid, palmitic acid, stearic acid, oleic acid and behenic acid and mixtures thereof. Examples of the above higher alcohols include dodecyl alcohol, lauryl alcohol, palmityl alcohol, stearyl alcohol and behenyl alcohol. Examples of the above paraffin waxes include natural paraffins, microcrystalline waxes, synthetic paraffins and chlorinated hydrocarbons. Examples of the above amide waxes include stearamide, oleamide, behenamide, methylenebisstearamide, ethylenebisstearamide, N,N'-m-xylylenebisstearamide, N,N -m-xylylenebis-12-hydroxystearamide, N,N -isophthalic acidbisstearylamide and N,N'-isophthalic acidbis-12-hydroxystearylamide. Examples of the above polyhydric alcohol esters include glycerin stearate, propylene glycol monostearate and sorbitan trioleate. Examples of the above silicone varnishes include methyl silicone varnish and phenyl silicone varnish. Examples of the above aliphatic fluorocarbons include low polymerized compounds of tetrafluoroethylene and hexafluoropropylene and fluorinated surfactants disclosed in JP-A-124428/1978. Among the above offset inhibitors, polyolefins are preferred, with polypropylene being particularly preferred.

Preferably, offset inhibitors are used in a proportion of 1 to 20 wt.%, based on the resin contained in the core material.

In the present invention, a colorant is contained in the core material of the capsule toner, and any of the conventional dyes or pigments that have been used as colorants for toners can be used.

Examples of the colorants used in the present invention include various carbon blacks which can be prepared by a thermal carbon black process, an acetylene black process, a channel black process and a lamp black process; a grafted carbon black in which the surface of the carbon black is coated with a resin; a nigrosine dye, phthalocyanine blue, Permanent Brown FG, Brilliant Fast Scarlet, Pigment Green B, Rhodamine-B Base, Solvent Red 49, Solvent Red 146 and Solvent Blue 35 and the mixtures thereof. The colorant is usually used in a Amount of about 1 to 15 parts by weight, based on 100 parts by weight of the resin contained in the core material, is used.

A magnetic capsule toner can be prepared by adding a particulate magnetic material to the core material. Examples of the particulate magnetic materials include ferromagnetic metals such as iron, i.e. ferrite or magnetite, cobalt and nickel, alloys thereof and compounds containing these elements; alloys containing no ferromagnetic element which become ferromagnetic by appropriate thermal treatment, for example, so-called "Heusler alloys" containing manganese and copper such as a manganese-copper-aluminum alloy and a manganese-copper-tin alloy, and chromium dioxide, with the compounds containing ferromagnetic materials being preferred, and magnetite being particularly preferred. Such a magnetic material is uniformly dispersed in the core material in the form of a fine powder having an average particle diameter of 0.1 to 1 µm. The content of these magnetic materials is 20 to 70 parts by weight, preferably 30 to 70 parts by weight, based on 100 parts by weight of the capsule toner.

When a particulate magnetic material is incorporated into the core material to prepare a magnetic toner, the material may be treated in a similar manner to the colorant. Since a particulate magnetic material as such has poor affinity to organic substances such as core materials and monomers, the material is used together with a known coupling agent such as a titanium coupling agent, a silane coupling agent or a lecithin coupling agent, with the titanium coupling agent being preferred, or treated with such a coupling agent before its use, thereby enabling the uniform dispersion of the particulate magnetic materials.

The encapsulated toner for heat and pressure fixing according to the present invention is preferably produced by the in-situ polymerization method from the viewpoint of simplifying the production devices and the production steps. The method for producing by the in-situ polymerization according to the present invention is described below.

In the method for producing the capsule toner according to the present invention, the shell can be produced by utilizing the property that when a mixed solution comprising the core material forming material and the shell forming material such as amorphous polyesters is dispersed in the aqueous dispersant, the shell forming material is localized on the surface of the liquid droplets. More specifically, the separation of the core material forming material and the shell forming material in the liquid droplets of the mixed solution occurs by the difference in solubility indexes, and polymerization proceeds in this state to form a capsule structure. With this method, since a shell is formed as a layer of the shell-forming materials containing an amorphous polyester as a main component with a substantially uniform thickness, the triboelectric charge of the obtained toner becomes uniform.

More specifically, the capsule toner of the present invention can be produced by the following steps (a) to (c):

(a) dissolving a shell-forming resin comprising an amorphous polyester as a main component in a mixture comprising a core material-forming monomer and a colorant;

(b) dispersing the mixture obtained in step (a) in an aqueous dispersant to form a polymerizable composition; and

(c) polymerizing the polymerizable composition obtained in step (b) by in-situ polymerization.

In the case of the above method, a dispersion stabilizer must be contained in the dispersion medium to prevent agglomeration and union of the dispersed substances.

Examples of the dispersion stabilizers include gelatin, gelatin derivatives, polyvinyl alcohol, polystyrenesulfonic acid, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, sodium carboxymethylcellulose, sodium polyacrylate, sodium dodecylbenzenesulfonate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium allylalkylpolyethersulfonate, sodium oleate, sodium laurate, sodium caprate, sodium caprylate, sodium caproate, potassium stearate, calcium oleate, sodium 3,3-disulfondiphenylurea-4,4-diazobisamino-β-naphthol-6-sulfonate, o-carboxybenzene azodimethylaniline, sodium 2,2,5,5-tetramethyltriphenylmethane-4,4-diazobis-β-naphthol disulfonate, colloidal silica, alumina, Tricalcium phosphate, iron (11) hydroxide, titanium hydroxide and aluminum hydroxide, with tricalcium phosphate and sodium dodecylbenzenesulfonate being preferred. These dispersion stabilizers may be used alone or in combination of two or more.

Examples of the dispersion media for the dispersion stabilizer include water, methanol, ethanol, propanol, butanol, ethylene glycol, glycerin, acetonitrile, acetone, isopropyl ether, tetrahydrofuran and dioxane, with water being preferred. These dispersion media may be used singly or in combination.

In the process of the present invention, the amount of the shell-forming material comprising the above amorphous polyester as a main component is 3 to 50 parts by weight, preferably 5 to 40 parts by weight, more preferably 8 to 30 parts by weight, based on 100 parts by weight of the core material. If it is less than 3 parts by weight, parts, the resulting shell becomes too thin in thickness, and the storage stability of the toner becomes poor. If it exceeds 50 parts by weight, the droplets dispersed in the aqueous dispersant have undesirably high viscosity, making it difficult to produce fine grains, which in turn results in poor production stability.

Here, the amount of the amorphous polyester having tertiary amine groups is the same as that of the amorphous polyester described above (the first embodiment).

In addition, for charge control, the charge control agents illustrated above may be appropriately added to the shell-forming materials of the capsule toner of the present invention. Alternatively, the charge control agent may be used in a mixture with a toner. In such a case, since the shell itself controls the chargeability, the amount of these charge control agents can be minimized if necessary.

Although the particle diameter of the capsule toner of the present invention is not particularly limited, the average particle diameter is usually 3 to 30 µm. The thickness of the shell of the capsule toner is preferably 0.01 to 1 µm. If the thickness of the shell is less than 0.01 µm, the blocking resistance of the obtained toner becomes poor, and if it exceeds 1 µm, the heat-fusibility of the obtained toner becomes undesirably poor.

In the capsule toner of the present invention, a flow improver or a cleanability improver may be used if necessary. Examples of the flow improvers include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, quartz sand, clay, mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide, ferric oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide and silicon nitride, with finely powdered silica being preferred.

The finely pulverized silica is a fine powder having Si-O-Si bonds, which can be prepared by either the dry process or the wet process. The finely pulverized silica may be not only anhydrous silica but also aluminum silicate, sodium silicate, potassium silicate, magnesium silicate and zinc silicate, with those containing not less than 85 wt% SiO₂ being preferred. Further, finely pulverized silica surface-treated with a silane coupling agent, titanium coupling agent, silicone oil and silicone oil having amine in its side chain may be used.

The agents for improving the cleaning ability include fine powders of metal salts of higher fatty acids, typical examples of which are zinc stearate or fluorocarbon polymers.

Furthermore, finely powdered polymers of methyl methacrylate or butyl methacrylate can be added to adjust the developability of the capsule toner.

Furthermore, a small amount of carbon black may be used to reduce the surface resistance of the toner. The carbon blacks may be selected from a variety of conventional carbon blacks such as furnace black, channel black and acetylene black.

When the capsule toner of the present invention contains a particulate magnetic material, it can be used alone as a developer, while when the capsule toner does not contain a particulate magnetic material, a non-magnetic one-component developer or a two-component developer can be prepared by mixing the toner with a carrier. Although the carrier is not particularly limited, examples thereof include iron powder, ferrite, glass beads, the above with resin coatings, and resin carriers in which magnetite fine powder or ferrite fine powder are mixed into the resins. The mixing ratio of the toner to the carrier is preferably 0.5 to 20% by weight. The particle diameter of the carrier is preferably 15 to 500 µm.

When the encapsulated toner of the present invention is fixed on a recording medium such as paper by heat and pressure, excellent fixing strength is obtained. As for the heat and pressure fixing method suitably used in fixing the toner of the present invention, any can be used as long as both heat and pressure are used. Examples of the fixing methods suitably used in the present invention include a known heat roller fixing method; a fixing method as disclosed in JP-A-190870/1990 in which visible images formed on a recording medium are fixed in an unfixed state by heating and melting the visible images through the heat-resistant sheet with a heating device comprising a heating part and a heat-resistant sheet, whereby the visible images are fixed on the recording medium; and a heating and printing method as disclosed in JP-A-162356/1990 in which formed visible images are formed on a recording medium through a film using a heating element mounted on a support and a pressing member arranged opposite to the heating element in contact therewith under pressure.

Since the above-described capsule toner according to the invention for heat and pressure fixing contains an amorphous polyester resin as the main component of the shell of the capsule toner it has excellent offset resistance and fixability even at low temperature, and also has excellent blocking resistance. Thus, clear images free from background contamination can be stably formed over a large number of copies in a heat and pressure fixing process using a heated roller. Also, by using the above specific amorphous polyester having positive charge instead of the above negatively charged amorphous polyester as the main component of the shell material of the capsule toner, the obtained toner has rapid triboelectric charging, stable positive charge, and also excellent offset resistance and fixability even at low temperature. Thus, clear images free from background contamination can be stably formed over a large number of copies in a heat and pressure fixing process using a heated roller.

Examples

The present invention will be described in detail below by the following working examples, comparative examples and test examples, but the present invention is not limited by these examples.

Resin preparation example 1:

367.5 g of a propylene oxide adduct of bisphenol A (average molar adduct number: 2.2, hereinafter abbreviated as "BPA·PO"), 146.4 g of an ethylene oxide adduct of bisphenol A (average molar adduct number: 2.2, hereinafter abbreviated as "BPA·EO"), 126.0 g of terephthalic acid (hereinafter abbreviated as "TPA"), 40.2 g of dodecenylsuccinic anhydride (hereinafter abbreviated as "DSA") and 17.7 g of trimellitic anhydride (hereinafter abbreviated as "TMA") are charged into a 2-liter four-necked flask equipped with a thermometer, stainless steel stirring bar, reflux condenser and nitrogen inlet tube, and heated to 220°C in a heating mantle under a nitrogen gas stream with stirring to react the above ingredients.

The degree of polymerization is monitored via a softening point measured according to ASTM E 28-67 and the reaction is stopped when the softening point reaches 110ºC. The resin is referred to as "Resin A".

Similar procedures to the above are carried out to prepare resins B and C. The compositions thereof are shown in Table 1. Also, the glass transition temperature of each of the resins thus obtained (resins A to C) is measured by a differential scanning calorimeter "DSC Model 220" manufactured by Seiko Instruments, Inc., and the values are shown in Table 2 together with the softening points and acid values. The acid values are measured by the method according to JIS K0070. Table 1

Resin preparation example 2:

630 g BPA·PO, 585 g BPA·EO, 780 g terephthalic acid dimethyl ester and 35 g of isophthalic acid are placed in a 3 L four-necked glass flask equipped with a thermometer, stainless steel stirring bar, reflux condenser and nitrogen inlet tube and heated in a heating mantle to 220ºC under a nitrogen gas stream with stirring to react the above ingredients.

The degree of polymerization is monitored by a softening point measured according to ASTM E 28-67. At the time when the softening point reaches 115ºC, 60 g of triethanolamine is added. The reaction is then continued at 200ºC and the reaction is stopped when the softening point reaches 110ºC. The amorphous polyester with tertiary amine groups thus obtained is referred to as "Resin D".

Resin Preparation Example 3:

630 g of BPA~PO, 585 g of BPA·EO and 600 g of TPA are placed in a 3 L four-necked glass flask equipped with a thermometer, stainless steel stirring rod, reflux condenser and nitrogen inlet tube and heated in a heating mantle at 220ºC under a nitrogen gas stream with stirring to react the above ingredients. The degree of polymerization is monitored by a softening point measured according to ASTM E 28-67. At the time when the softening point reaches 115ºC, 60 g of triethanolamine is added. The reaction is then continued at 200ºC and the reaction is stopped when the softening point reaches 110ºC. The amorphous polyester having tertiary amine groups thus obtained is referred to as "Resin E".

Resin Preparation Example 4:

630 g of BPA·PO, 23.8 g of N,N-bis(2-hydroxyethyl)methylamine and 190 g of succinic anhydride are placed in a 2 L four-necked glass flask equipped with a thermometer, stainless steel stirring bar, reflux condenser and nitrogen inlet tube and heated in a heating mantle to 220ºC under a nitrogen gas stream with stirring to react the above ingredients.

The degree of polymerization is monitored by a softening point measured according to ASTM E 28-67, and the reaction is stopped when the softening point reaches 110ºC. The amorphous polyester with tertiary amine groups thus obtained is referred to as "Resin F".

The glass transition temperature of each of the resins thus obtained (Resins D to F) is measured using the differential scanning calorimeter ("DSC Model 220", manufactured by Seiko Instruments, Inc.) and the values are shown in Table 2 along with the softening points, acid values and total amine values. The acid values are measured by the method specified in JIS K0070. The total amine values are measured by the method specified in ASTM D-2073-66. Table 2

Example 1:

20 parts by weight of Resin A and 3.5 parts by weight of 2,2'-azobisisobutyronitrile were added to a mixture comprising 69.0 parts by weight of styrene, 31.0 parts by weight of 2-ethylhexyl acrylate, 0.9 parts by weight of divinylbenzene and 7.0 parts by weight of carbon black "#44" (manufactured by Mitsubishi Kasei Corporation). The resulting mixture was charged into a stirrer (Model MA-OlSC, manufactured by Mitsui Müke Kakoki) and dispersed at 10°C for 5 hours to obtain a polymerizable composition. Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate prepared previously in a 2-liter separable flask. The resulting mixture is emulsified and dispersed with "T. K. HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo) at 15°C and a rotation speed of 12,000 rpm for 5 minutes.

Next, a four-neck glass cap is placed on the flask and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached thereto. The flask is placed in an electric heating mantle. Thereafter, the contents are heated to 85°C and reacted at 85°C for 10 hours in a nitrogen atmosphere with stirring. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The obtained product is filtered and the obtained solid is washed with water, dried under reduced pressure of 20 mm/l at 45°C for 12 hours and classified with an air sifter to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises an amorphous polyester. Here, the amorphous polyester has no tertiary amine groups.

To 100 parts by weight of this capsule toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain a capsule toner according to the present invention. This toner is referred to as "Toner 1". The glass transition temperature attributable to the resin contained in the core material is 30.6°C, and the softening point of the Toner 1, determined by a flow tester, is 125.5°C.

Here, the "softening point determined by a flow tester" used refers to the temperature corresponding to half the height (h) of the S-shaped curve showing the relationship between the downward movement of a punch (flow length) and the temperature measured using a "Koka" type flow tester manufactured by Shimadzu Corporation in which a sample of 1 cm³ is passed through a nozzle having a nozzle opening size of 1 mm and a length of 1 mm under Heating the sample so as to increase the temperature at a rate of 6ºC/min and applying a load of 20 kg/cm² is extruded with the punch.

Example 2:

100 parts by weight of a copolymer obtained by copolymerizing 75 parts by weight of styrene and 25 parts by weight of n-butyl acrylate, the copolymer having a softening point of 75.3°C and a glass transition temperature of 40.5°C, is premixed together with 6 parts by weight of copper phthalocyanine "Sumikaprint Cyanine Blue GN-O" (manufactured by Sumitomo Chemical Co:; Ltd.), 15 parts by weight of Resin B and 5 parts by weight of polypropylene wax "Viscol 550p" (manufactured by Sanyo Chemical Industries, Ltd.), and melt-kneaded in a twin-screw extruder, cooled and pulverized. 40 parts by weight of this kneaded mixture are mixed with 50 parts by weight of styrene, 15 parts by weight of n-butyl acrylate and 2.5 parts by weight of 2,2'-azobisisobutyronitrile to obtain a polymerizable composition.

Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate prepared in advance in a 2-liter separable glass flask. The resulting mixture is emulsified and dispersed using a "T. K. HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo) at 15°C and a rotation speed of 12,000 rpm for 2 minutes.

Next, a four-neck glass cap is placed on the flask and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached thereto. The flask is placed in an electric heating mantle. After that, the contents are heated to 85°C and reacted at 85°C for 10 hours in a nitrogen atmosphere with stirring. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The obtained product is filtered and the obtained solid is washed with water, dried under reduced pressure of 20 mmHg at 45°C for 12 hours and classified with an air classifier to obtain a capsule toner having an average particle size of 8 µm whose shell comprises an amorphous polyester. Here, the amorphous polyester has no tertiary amine groups.

To 100 parts by weight of this capsule toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain a capsule toner according to the invention. This toner is referred to as "Toner 2". The glass transition temperature attributable to the resin contained in the core material is 33.2ºC and the softening point of toner 2, determined with a flow tester, is 122.8ºC.

Example 3:

20 parts by weight of resin C and 5.0 parts by weight of lauroyl peroxide are added to a mixture comprising 50 parts by weight of styrene, 35.0 parts by weight of 2-ethylhexyl acrylic acid ester, 1.0 part by weight of divinylbenzene, 1.0 part by weight of dimethylaminoethyl methacrylate and 40.0 parts by weight of styrene-grafted carbon black "GP-E-3" (manufactured by Ryoyu Kogyo) to obtain a polymerizable composition

Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate prepared in advance in a 2-liter separable glass flask. The resulting mixture is emulsified and dispersed at 15°C and a rotation speed of 12,000 rpm for 5 minutes with "T. K. HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo).

Next, a four-neck glass cap is placed on the flask and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached thereto. The flask is placed in an electric heating mantle. Thereafter, the contents are heated to 85°C and reacted at 85°C for 10 hours in a nitrogen atmosphere with stirring. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The obtained product is filtered and the obtained solid is washed with water, dried under reduced pressure of 20 min at 45°C for 12 hours and classified with an air classifier to obtain a capsule toner having an average particle size of 8 tm, the shell of which comprises an amorphous polyester. Here, the amorphous polyester has no tertiary amine groups.

To 100 parts by weight of this capsule toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain the capsule toner of the present invention: This toner is referred to as "Toner 3". The glass transition temperature attributable to the resin contained in the core material is 33.5°C, and the softening point of Toner 3, determined by a flow tester, is 124.3°C.

Example 4:

18 parts by weight of resin A, 2.0 parts by weight of a copolymer obtained by copolymerizing maleic anhydride and styrene (molar ratio of maleic anhydride : styrene = 1 : 3; molecular weight: 1900; glass transition temperature: 124.7ºC) and 3.5 parts by weight of 2,2'-azobisisobutyronitrile is added to a mixture comprising 65.0 parts by weight of styrene, 35.0 parts by weight of 2-ethylhexyl acrylate, 0.9 parts by weight of divinylbenzene and 7.0 parts by weight of carbon black "#44" (manufactured by Mitsubishi Kasei Corporation). The resulting mixture is charged into a stirrer (Model MA-01SC, manufactured by Mitsui Müke Kakoki) and dispersed at 10°C for 5 hours to obtain a polymerizable composition.

Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate prepared in advance in a 2-liter separable glass flask. The resulting mixture is emulsified and dispersed with "T. K. HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo) at 15°C and a rotation speed of 12,000 rpm for 5 minutes.

Next, a four-neck glass cap is placed on the flask, and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached thereto. The flask is placed in an electric heating mantle. After that, the contents are heated to 85°C and reacted at 85°C for 10 hours in a nitrogen gas stream with stirring. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The obtained product is filtered, and the obtained solid is washed with water, dried under reduced pressure of 20 mmHg at 45°C for 12 hours and classified with an air classifier to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises an amorphous polyester and a copolymer having one or more acid anhydride groups as main components. Here, the amorphous polyester has no tertiary amine groups.

To 100 parts by weight of this capsule toner, 0.4 part by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain the capsule toner of the present invention. This toner is referred to as "Toner 4". The glass transition temperature attributable to the resin contained in the core material is 30.2°C, and the softening point of Toner 4, determined by a flow tester, is 122.8°C.

Example 5:

20 parts by weight of resin D and 3.5 parts by weight of 2,2-azobisisobutyronitrile are added to a mixture comprising 69.0 parts by weight of styrene, 31.0 parts by weight of 2-ethylhexyl acrylate, 0.9 parts by weight of divinylbenzene and 7.0 parts by weight of carbon black "#44" (manufactured by Mitsubishi Kasei Corporation). The resulting mixture is placed in a stirrer (Model MA-OISC, manufactured by Mitsui Müke Kakoki) and stirred for 5 hours at 15ºC to obtain a polymerizable composition.

Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate previously prepared in a 2-liter separable glass flask. The resulting mixture is emulsified and dispersed with "T. K. HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo) at 15°C and a rotation speed of 12,000 rpm for 5 minutes.

Next, a four-neck glass cap is placed on the flask and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached thereto. The flask is placed in an electric heating mantle. Thereafter, the contents are heated to 85°C and reacted at 85°C for 10 hours in a nitrogen atmosphere with stirring. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The obtained product is filtered and the obtained solid is washed with water, dried under reduced pressure of 20 mmHg at 45°C for 12 hours and classified with an air classifier to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises an amorphous polyester having tertiary amine groups.

To 100 parts by weight of this capsule toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain the capsule toner of the present invention. This toner is referred to as "Toner 5". The glass transition temperature attributable to the resin contained in the core material is 32.7°C, and the softening point of Toner 5, determined by a flow tester, is 119.2°C.

Example 6:

20 parts by weight of carbon black "GPT-505P" (manufactured by Ryoyu Kogyo) is added to a mixture comprising 69.0 parts by weight of styrene, 31.0 parts by weight of 2-ethylhexyl acrylate, 0.7 parts by weight of divinylbenzene, 4.0 parts by weight of 2,2'-azobisisobutyronitrile and 20 parts by weight of Resin E, and the resulting mixture is dispersed for 1 hour using a magnetic stirrer to obtain a polymerizable composition.

Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate previously prepared in a 2-liter separable glass flask. The resulting mixture is mixed with "TK HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo) at 15ºC and a rotation speed of 10000 rpm for 2 minutes.

Next, a four-neck glass cap is placed on the flask and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached thereto. The flask is placed in an electric heating mantle. Thereafter, the contents are heated to 85°C and reacted at 85°C for 10 hours in a nitrogen atmosphere with stirring. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The obtained product is filtered and the obtained solid is washed with water, dried under reduced pressure of 20 mIl-Ig at 45°C for 12 hours and classified with an air sizing device to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises an amorphous polyester having tertiary amine groups.

To 100 parts by weight of this capsule toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain the capsule toner of the present invention. This toner is referred to as "Toner 6". The glass transition temperature attributable to the resin contained in the core material is 29.5°C, and the softening point of Toner 6, determined by a flow tester, is 123.3°C.

Example 7:

Similar procedures to those of Example 6 are carried out up to the surface treatment step except that 20 parts by weight of resin E are replaced by 15 parts by weight of resin D and 5 parts by weight of resin A, to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises an amorphous polyester having tertiary amine groups as a main component. This toner is referred to as "Toner 7". The glass transition temperature attributable to the resin contained in the core material is 26.8°C, and the softening point of Toner 7, determined by a flow tester, is 119.8°C.

Example 8:

Similar procedures to those of Example 5 are carried out up to the surface treatment step except that 20 parts by weight of Resin D is replaced by 20 parts by weight of Resin F, to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises an amorphous polyester having tertiary amine groups as a main component. This toner is referred to as "Toner 8". The glass transition temperature attributable to the resin contained in the core material is 32.5°C, and the softening point of Toner 8, determined by a flow tester, is 120.5°C.

Comparison example 1:

3.5 parts by weight of 2,2'-azobisisobutyronitrile and 9.5 parts by weight of 4,4'-diphenylmethane diisocyanate "Millionate MT" (manufactured by Nippon Polyurethane Industry Co., Ltd.) are added to a mixture comprising 70.0 parts by weight of styrene, 30.0 parts by weight of 2-ethylhexyl acrylic acid ester, 1.0 part by weight of divinylbenzene and 10.0 parts by weight of carbon black "#44" (manufactured by Mitsubishi Kasei Corporation). The resulting mixture is placed in a stirrer (Model MA-OISC, manufactured by Mitsui Müke Kakoki) and dispersed at 10°C for 5 hours to obtain a polymerizable composition.

Next, 240 g of the above polymerizable composition is added to 560 g of a 4 wt% aqueous colloidal solution of tricalcium phosphate prepared in advance in a 2-liter separable glass flask. The resulting mixture is emulsified and dispersed with "T. K. HOMO MIXER, Model M" (manufactured by Tokushu Kika Kogyo) at 15°C and a rotation speed of 12,000 rpm for 2 minutes.

Next, a four-neck glass cap is placed on the flask and a reflux condenser, thermometer, nitrogen inlet tube and stainless steel stirring rod are attached to it. The flask is placed in an electric heating mantle. A solution of a mixture containing 7.5 parts by weight of ethylenediamine, 0.5 part by weight of dibutyltin dilaurate and 40 g of ion-exchanged water is prepared and the resulting mixture is dropped into the flask through the dropping funnel over a period of 30 minutes with stirring. Thereafter, the contents are heated to 80°C and reacted for 10 hours in a nitrogen atmosphere with stirring at 80°C. After cooling the reaction product, the dispersant is dissolved in 10% aqueous hydrochloric acid. The product obtained is filtered and the solid obtained is washed with water, dried at 45°C for 12 hours under a reduced pressure of 20 mmHg and then classified with an air classifier to obtain a capsule toner having an average particle size of 8 µm, the shell of which comprises a polyurea resin.

To 100 parts by weight of this capsule toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain a capsule toner. This toner is referred to as "Comparative Toner 1". The glass transition temperature attributable to the resin contained in the core material is 33.5°C, and the softening point of the comparative toner determined by a flow tester is 137.0°C.

Comparison example 2:

Similar procedures to those of Example 1 are carried out up to the step of washing the solid obtained by filtration after the polymerization reaction step with water, except that Resin A is not used. It is dried under a reduced pressure of 10 mm³ at 20°C for 12 hours and classified with an air classifier to obtain a non-encapsulated toner having an average particle size of 8 µm.

To 100 parts by weight of this non-encapsulated toner, 0.4 parts by weight of hydrophobic silica fine powder "Aerozil R-972" (manufactured by Nippon Aerozil Ltd.) is added and mixed to obtain a toner. This toner is referred to as "Comparative Toner 2". The glass transition temperature attributable to the resin contained in the core material is 30.5°C, and the softening point of Comparative Toner 2, determined by a flow tester, is 115.5°C.

Test example 1:

A developer is prepared by placing 6 parts by weight of each of the toners obtained in Examples 1 to 4 and Comparative Examples 1 and 2 and 94 parts by weight of spherical ferrite powder coated with styrene-methyl methacrylate copolymer resin having a particle size between 400 mesh and 250 mesh in a polyethylene container and mixing the above ingredients by rotating the container on the roller at a rotation speed of 150 rpm for 20 minutes. The obtained developer is evaluated for triboelectric charge, fixability, offset resistance and blocking resistance.

(1) Triboelectric charge

The triboelectric charge is measured by a blow-off type electric charge measuring device as described below. More specifically, a specific charge measuring device equipped with a Faraday cage, capacitor and electrometer is used. First, W (g) (about 0.15 to 0.20 g) of the developer prepared above is placed in a brass measuring cell equipped with a 500 mesh stainless steel screen adjustable to any mesh size to block the passage of the carrier particles. Next, after suction from a suction port for 5 seconds, blowing is carried out for 5 seconds under a pressure of 0.6 kgf/cm2 specified by a barometric control device, whereby only the toner is selectively removed from the cell.

In this case, the voltage of the electrometer after 2 seconds from the beginning of blowing is defined as V (Volt). Here, if the electrical capacity of the capacitor is defined as C (PF), the triboelectric charge Q/m of this toner can be calculated by the following equation:

Q/m (uC/g) = C x V/m

Here, m is the weight of toner contained in W(g) of the developer. If the weight of toner in the developer is defined as T(g) and the weight of the developer is defined as D(g), the toner concentration in a certain sample can be expressed as T/D x 100 (%) and m can be calculated as shown in the following equation:

m (g) = W x (T/D)

The measurement results of the triboelectric charge of the developer prepared under normal conditions are shown in Table 3.

In addition, the triboelectric charge of the toners after copying 50,000 sheets is measured by placing each of the developers in a commercially available electrophotographic copier (equipped with a selenium-arsenic photoconductor for toners 1, 2, 4 and comparative toner 2 or an organic photoconductor for toner 3 and comparative toner 1; a fixing roller with a rotation speed of 255 mm/s; and a toner concentration of 6%). The results are shown in Table 3. Also, the image quality determined by the amount of background generated during the continuous copying test and the toner dust in the apparatus are evaluated and are shown together in Table 3. Table 3

(2) Fixability

Fixability is assessed using the method described below.

More specifically, each of the developers prepared as described above is charged into a commercially available electrophotographic copier to develop images. The copier is equipped with a selenium-arsenic photoconductor for toners 1, 2, 4 and comparative toner 2 or an organic photoconductor for toner 3 and comparative toner 1; a fixing roller having a rotation speed of 255 mm/s; a fixing device having variable heat and pressure and temperature; and an oil applicator was removed from the copier. Setting the fixing temperature from 70°C to 220°C, the fixability of the formed images is evaluated. The results are shown in Table 4.

The lowest fixing temperature used here is the temperature of the fixing roller at which the fixing ratio of the toner exceeds 70%. This fixing ratio of the toner is determined by applying a load of 500 g to a sand-based rubber eraser (LION No. 502) with a bottom area of 15 mm x 7.5 mm, which is the fixed toner image, placing the eraser with load on a fixed toner image obtained in the fixing device, moving the eraser with load back and forth on the image five times, measuring the reflection optical density of the image treated with the eraser with the reflection density meter manufactured by Macbeth Co., and then calculating the fixing ratio from this density value and a density value before treatment with the eraser using the following equation.

Fixing ratio = Image density after eraser treatment / Image density before eraser treatment · 100

(3) Offset resistance

Offset resistance is evaluated by measuring the offset disappearance temperature at low temperature and the offset initiation temperature at high temperature using the same test apparatus under the same test conditions as in the fixability test. Specifically, copying tests are conducted while increasing the temperature of the heat roller surface with an increment of 5ºC in the range of 70ºC to 220ºC, and at each temperature, the adhesion of the toner to the surface of the heat roller for fixing is evaluated with the naked eye.

The results are also shown in Table 4.

(4) Blocking resistance

The blocking resistance is determined by determining the extent of generation of agglomeration of particles after allowing the toner to stand under a temperature of 50ºC and a relative humidity of 40% for 24 hours. The results are also shown in Table 4. Table 4

As is clear from Table 3, with respect to the inventive toners 1 to 4 and the comparative toner 1, the values of the triboelectric charges are reasonable since they show little change in triboelectric charge after copying 50,000 sheets while maintaining excellent image quality. However, in the comparative toner 2, since toning of the toner on the carrier occurs, its polarity is reversed after copying 50,000 sheets. In addition, when the comparative toner 2 is used, the image contamination by high background occurs during the copying process presumably by the generation of a large number of reversely charged particles, and toner dust in the copier also occurs. Further, as is clear from Table 4, in the toners 1 to 4, all have low minimum fixing temperatures and wide non-offset ranges. However, in Comparative Toner 1, since the melting point of the polyurea resin used as the shell material is high (more than 300ºC), its lowest fixing temperature is high (200ºC). Since Comparative Toner 2 is composed of the core material of Toner 1 alone, it has poor blocking resistance.

Test example 2:

Each of the toners obtained in Examples 5 to 8 is evaluated for storage stability, triboelectric charge, fixability and offset resistance. (1) Storage stability

The storage stability is determined by measuring 5 g of each toner into an aluminum cup with a diameter of 90 mm, leaving it for 24 hours at a temperature of 50ºC and a relative humidity of 40%, and evaluating the extent of generation of agglomeration. The results are shown in Table 5. Table 5

(2) Triboelectric charge

A developer is prepared by placing 4 parts by weight of each of the toners obtained in Examples 5 to 8 and 96 parts by weight of spherical ferrite powder coated with phenyl silicone resin having a particle size of 400 mesh to 250 mesh in a polyethylene container and mixing the above ingredients by rotating the container on a roller at a rotation speed of 150 rpm for 20 minutes. The resulting developer is evaluated for triboelectric charge.

The triboelectric charge is measured with an electric charge measuring device of the blow-off type as described above in Test Example 1. Each developer is charged into a commercially available electrophotographic copier (equipped with an organic photoconductor; a fixing roller with a rotation speed of 255 mm/s and a toner concentration of 4%). The results are shown in Table 6 together with those measured after copying 50,000 sheets.

Also, the image density and image quality determined by the amount of background and toner dust generated in the device during the continuous copy test were measured and shown together in Table 6. Table 6

(3) Fixability

Fixability is determined using the method described above.

Specifically, each of the developers prepared as above is charged into a commercially available electrophotographic copier to develop images. The copier is equipped with an organic photoconductor; a fixing roller having a rotation speed of 255 mm/s; a fixing device with variable heat and pressure and temperature, and an oil applying device was removed from the copier. By controlling the fixing temperature from 70°C to 220°C, the fixability of the formed images is evaluated as in Test Example 1. The results are shown in Table 7.

(4) Offset resistance

The offset resistance is determined as in Test Example 1 by measuring the low-temperature offset disappearance temperature and the high-temperature offset initiation temperature using the same test apparatus under the same test conditions as in the fixability test. The results are also shown in Table 7. Table 7

As is clear from Tables 5 to 7, the toners 5 to 8 show high values of triboelectric charge at the beginning and also show only a small change in triboelectric charge after copying 50,000 sheets, thus showing excellent stability of triboelectric charge. Also, they show only small changes in image density and image quality, toner dust in the copier does not occur, and furthermore they show excellent storage stability. Furthermore, in toner 7 using an amorphous polyester having tertiary amine groups together with an amorphous polyester without tertiary amine groups, the positive electric charge can be well controlled. In addition, toners 5 to 8 all show low minimum fixing temperatures and wide non-offset ranges, while exhibiting excellent fixability.

Claims (10)

1. A capsule toner for heat and pressure fixation comprising a heat-fusible core material containing at least a thermoplastic resin and a colorant, and a shell formed thereon so as to cover the surface of the core material, wherein the shell comprises an amorphous polyester as a main component, the amorphous polyester optionally having tertiary amine groups, and the amount of the amorphous polyester is 3 to 50 parts by weight based on 100 parts by weight of the core material, and the amorphous polyester has a glass transition temperature of 50°C to 80°C, and the glass transition temperature attributable to the thermoplastic resin used as a main component of the heat-fusible core material is 10°C to 50°C. 2. The heat and pressure fixing capsule toner according to claim 1, wherein the shell consists essentially of the amorphous polyester. 3. The encapsulated toner for heat and pressure fixing according to claim 1, wherein the shell comprises the amorphous polyester and a copolymer having one or more acid anhydride groups. 4. The encapsulated toner for heat and pressure fixation according to any one of claims 1 to 3, wherein the amorphous polyester is obtainable by condensation polymerization of monomers comprising a dihydric alcohol monomer and a dicarboxylic acid monomer, and further at least one trihydric or higher polyhydric alcohol monomer and/or a tricarboxylic acid or higher polycarboxylic acid monomer. 5. Capsule toner for heat and pressure fixation according to one of claims 1 to 4, wherein the amorphous polyester has an acid number of 3 to 50 KOH mg/g. 6. Capsule toner for heat and pressure fixation according to one of claims 1 to 5, wherein the amorphous polyester having tertiary amine groups is obtainable by a condensation polymerization of a monomer mixture comprising a monomer having one or more tertiary amine groups, and wherein the monomer having one or more tertiary amine groups is one or more monomers selected from divalent or higher polyvalent alcohol monomers and dicarboxylic acid or higher polycarboxylic acid monomers having the chemical structures of the following general formulas (I), (IIA), (IIB) and (III) and the divalent or higher polyvalent alcohol monomers by the following general formulas (I), (IIA), (IIB), (III) and (IV) are reproduced: wherein R₁, R₂, R�5, R�7, R�8, R�9, R₁₀, R₁₁₀, R₁₁₁, R₁₁₄, R₁₃, R₁₄ and R₁₆ independently represent a hydrocarbon group having 1 to 15 carbon atoms; R₃ and R₄ independently represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms; R₆ represents an alkyl, cycloalkyl, alkylene or cycloalkylene group having 1 to 10 carbon atoms; R₁₅ represents an alkyl group having 1 to 3 carbon atoms or R₁₇ and R₁₈ independently represent an alkyl group having 1 to 4 carbon atoms, wherein R₁₇ and R₁₈ may form a heterocyclic ring with the nitrogen atom; and X represents a hydrogen atom or a hydroxyl group. 7. The heat and pressure fixing capsule toner according to claim 6, wherein the amount of the monomer having one or more tertiary amine groups used is 1 to 30 mol% based on the total monomers. 8. Capsule toner for heat and pressure fixation according to one of claims 1 to 7, wherein the amorphous polyester with tertiary amine groups has an acid number of 1 to 50 KOH mg/g. 9. Capsule toner for heat and pressure fixation according to one of claims 1 to 8, wherein the amorphous polyester with tertiary amine groups has an amine number of 2 to 25 KOH mg/g. 10. A method for producing a capsule toner for heat and pressure fixing comprising a heat-fusible core material containing at least a thermoplastic resin and a colorant and a shell formed thereon so as to to cover the surface of the core material, comprising the following steps (a) to (c): (a) dissolving a shell-forming resin comprising an amorphous polyester optionally having tertiary amine groups as a main component in a mixture comprising a core material-forming monomer and a colorant, the amount of the amorphous polyester being 3 to 50 parts by weight based on 100 parts by weight of the core material, the amorphous polyester having a glass transition temperature of 50°C to 80°C and the glass transition temperature attributable to the thermoplastic resin used as a main component of the heat-fusible core material being 10°C to 50°C; (b) dispersing the mixture obtained in step (a) in an aqueous dispersant to obtain a polymerizable composition; and (c) polymerizing the polymerizable composition obtained in step (b) by in-situ polymerization.